1. Field of the Invention
The present invention relates to a sheet discharging apparatus used in a printer processor, an automatic development system, an image recording apparatus and the like, and particularly to a sheet discharging equipment for discharging recording sheets arranged in zigzag among rows so as to align in one row.
2. Description Related to the Prior Art
In a printer processor used in a photo laboratory is used a paper roll in which a continuous photosensitive recording paper is rolled. The photosensitive recording paper which is advanced from the paper roll is cut into recording sheets, and each recording paper is exposed so as to form an image. In the printer processor, thereafter, the recording sheet is transported to a development device in which the development and the fixation are made and a dryer in which the drying is made. As the recording sheet, there are a photosensitive recording sheet, normal paper sheet, and the like. And the recording sheet is simply called a sheet.
Compared with the exposing treatment for exposing and recording the image, a long time period is necessary to perform the developing treatment of one sheet in the development device, since during the developing treatment the sheet is conveyed through processing tanks which respectively contain water and processing liquids for color development, bleaching, fixation, wash, and stabilization. Accordingly, before the developing treatment in the development device, plural exposed sheets are dispensed so as to lie in zigzag in the plural rows in the conveying path such that the sheet of the latter exposure may be positioned behind that of the former exposure. Then the exposed sheets are conveyed to the development device. As the development is made after the zigzag arrangement of the sheets in plural rows on the conveying path, the facility of the treatment becomes larger in the same treatment period. Further, the sheet after the developing treatment is conveyed with the arrangement in the plural rows on the conveying path, and supplied in the dryer. In the dryer, an air heated by a heater is blown with fans so as to dry the sheet.
Otherwise, after the developing treatment and the drying treatment, the sheets discharged in plural rows as described above are gathered into a dispenser with the arrangement in a single row of the sheets in the order of the exposure. For example, Japanese Patents No. 3286598 (Pages 1–2), 2812143 (Pages 1–2), 2765652 (Pages 2–4), and Japanese Patent Publication No. 60-23343 (Page 1) describe a sheet discharging apparatuses, in each of which the sheets conveyed in the plural rows are discharged and arranged in a single row in the order of the exposure.
In the sheet discharging apparatus described in the publications, there are a conveying path for conveying the plural sheets arranged in plural rows, a discharging means which is disposed near an entrance of the conveying path and discharges out at a high speed the sheets conveyed in the plural rows, and a conveyer whose endless belt continuously shifts in a direction perpendicular to the discharging direction of the discharging means and surmounts the sheets discharged by the discharging means. When the sheets are surmounted on the belt, they reach sequentially in the order of the exposure, and therefore they are conveyed on the endless belt in the single row.
In such sheet discharging apparatus, when the sheet is discharged at a high speed to the endless belt by the discharging means, the rear edge of the sheet is nipped by a roller pair for conveying the sheet in the plural rows, and there is a difference between the conveying speed of the roller pair and the discharging speed of the discharging means. Accordingly, in order to discharge at high speed to the endless belt, it is necessary to eliminate the difference. In the above publications No. 3286598 and 2812143, the sheet discharging apparatus is provided with a one-way clutch between a conveyer roller of the roller pair disposed along the plural rows and a shaft for coaxially supporting the conveyer rollers. When the discharging at the high speed to the endless belt is performed, the one-way clutch operates to release the conveyer roller from the driving system. Thus the conveyer roller freely rotates such that the sheet may smoothly leave the roller pair.
However, in order to eliminate the difference between the conveying speed of the conveying roller and the discharging speed by the discharging means in this structure of free rotation of the conveying roller by the effect of the one-way clutch, a large number of the one-way clutches is provided in accordance with the length variation of the cut sheet to be used in the above sheet discharging apparatus. As the one-way clutch is expensive, a low cost for production is difficult. Further, as the one-way clutch is attached to one roller of the conveyer roller pair, the roller nip force of the other roller of the conveyer roller pair is applied as a bending moment and an excess radial load to the one-way clutch and the conveyer roller, and therefore breaks the one-way clutch. Therefore, the durability of such a clutch is not so high.
In the publication No. 2765652, a torque limiter is provided between a drive shaft and a drive roller of a high speed discharging means. The torque limiter operates to freely rotate the drive roller, when a torque applied to the drive roller is at least a predetermined value. Thus the difference between the conveying speed of the conveyer roller and the discharging speed of the drive roller of the discharging means is eliminated. The drive roller is supported by a frame attached to the drive shaft. There is also a gear drive transmission mechanism between the drive roller and the drive shaft. Thus the drive force of the drive shaft is transmitted through the gear drive transmission mechanism and the torque limiter to the drive roller. Accordingly, the structure around the drive roller is complicated, the cost is high, and it is hard to keep the area for deposition of the parts. Further, the torque limiter is the so-called magnetic particle type, and therefore expensive, which make the cost higher. Furthermore, in the publication No 60-23343, a clutch mechanism which is constructed of a solenoid and a pair of clutch plates is used instead of the one-way clutch and the torque limiter. In this case, however, the number of the parts becomes larger, and many controlling means are necessary, which prevents decrease of the cost.